In the construction of factory-built housing, economies are created by using production line techniques. As may be readily appreciated, a great deal of wallboard must be cut in a variety of shapes and sizes in order to build the inner walls and ceilings of such dwellings. Since there is a substantial amount of standardization, the shapes, sizes and number of pieces of wallboard or drywall that must be employed on a given production run may be determined quite accurately. Heretofore, however, it has not been possible to take full advantage of this knowledge because the desired cutting machinery was not available. When used on drywall, standard table saws created so much dust and the saw blades wore out so rapidly that maintenance and cleaning costs and health hazards outweighed their advantages. In addition, the only table saw known to the inventors to be especially adapted to score and cut drywall had a single pair of power driven rotary blades and thus was not much faster to use than hand-operated cutters.
The closest prior art known to the inventors are U.S. Pat. Nos. Re. 30,324 reissued July 8, 1980 to Seme; 3,610,079 issued Oct. 5, 1971 to Ashby; and 2,529,210 issued Nov. 7, 1950 to Butler. Seme discloses a device for forming score lines in a thin sheet of metal. The Seme scoring device is provided with upper and lower rotatable shafts on each of which is mounted a plurality of circular blades. While the relative positions and number of blades on each shaft may be changed, the means for doing so are cumbersome. In addition, the blades are not freely rotatable and either one or both of the shafts is power driven. While driven blades may be suitable for scoring relatively small pieces of metal, they tend to inject gypsum dust into the air when employed to cut wallboard. Ashby discloses a portable cutter provided with a pair of straight blades or knives that eliminate the dust problem, but the Ashby cutter cannot make multiple cuts simultaneously in the drywall. The blades are secured to pivotal arms extending from slides that move along upper and lower guide rails. Additional blade-bearing slides cannot be added because the existing pair of slides are rigidly secured to upper and lower handle bars by which their positions relative to the drywall workpiece are controlled. In addition, the blades tend to wear our quickly. Butler discloses cutter-bearing slides that are mounted in guide channels having relatively unobstructed ends, but the Butler device, like the Ashby cutter, is provided with straight blades or knives and is not adapted to make multiple cuts or scores in a sheet of wallboard. Thus, the Ashby and Butler drywall cutters are relatively portable, hand-operated tools more suited to on site construction work than to mass production. Likewise, the Seme device appears to be well suited for scoring metal plates, but not for scoring or cutting drywall.
Portable or hand operated drywall cutters are not practical in factory environments because they do not provide enough assistance to the operator and are not sturdy enough to withstand sustained use. Full size sheets of wallboard are so heavy and cumbersome that, absent substantial mechanical assistance, an average worker who handles such sheets repeatedly will tire rapidly. The cardboard and crushed gypsum stone of which the wallboard is composed require the application of a substantial amount of force to draw a hand-operated cutting tool through just the surface portions thereof. In addition, these materials tend to wear out straight knife blades rapidly. Thus, the present inventors were faced with a need for a heavy duty drywall cutter that would relieve the operator of lifting and moving the drywall, drawing the blade through opposing surfaces, making multiple cuts, and replacing the blades frequently.